Preventing the development of sourness in certain petroleum liquids during distillation



tive boiling ranges are as follows: ether, 90-140 F., special textile spirits, 180-210 Patented Feb. 23, 1954 UNITED STATES PATENT OFFICE PREVENTING THE DEVELOPMENT OF SOUR- NESS IN CERTAIN PETROLEUM LIQUIDS DURING DISTILLATION No Drawing. Application April 14, 1950, Serial No. 156,036

Claims. 1

The present invention relates to the physical separation of specialty products from light petroleum distillates comprising parts of the gasoline and kerosene boiling range or both. It is more particularly concerned with a method for obviating the need for retreating special naphtha products which have been fractionally distilled. from a naphtha feed stock, which has been sweetened in an oxidation treating process for mercaptan conversion prior to separating the special naphtha products.

The petroleum industry of today is no longer solely concerned with the production of fuels and lubricants. Due to the increased demand of manufacturers for solvents, chemicals and other articles of commerce available from the petroleum industry, the modern refining industry must be capable of diversification in its production of marketable products. The availability of petroleum hydrocarbons for chemical processing has given rise to the petrochemical industry which, in 1948, accounted for about percent of the production of synthetic organic chemicals. Although products which can be represented by specific chemical symbols are generally classified as petrochemical, what might be included as a facet of the petrochemical category of petroleum products are the hydrocarbon solvents, such as rubber solvent, V. M. and P. naphtha and Stoddard solvent. These particular specialty refinery signed to ,meet the specifications of individual consumers, or to suit a specific need. A few specific examples of these commercially available specialized petroleum products and their respec- Petroleum -.-protective coating industry, the natural and synthetic rubber industry, solvent extractionv and other miscellaneous industries. Specific applicaticns include use as solvents in paints, varnishes- I and lacquers; rubber cements. and adhesives; ex-

traction of fats-both vegetable and mineral. To meet the requirements of this growing demand,

' the potential naphthas contained, in available crude stocks were found especially satisfactory.

The almost limitless variety of boiling ranges and solvencies available from a petroleum naphtha having a boiling range from about 225 to 425 F. obtained from a paraffin, naphthene or intermediate base crude makes its use as a feed stock to be employed in a special naphtha rerun unit which produces these special naphtha products ideal. Since straight run petroleum naphthas contain only small amounts of aromatic hydrocarbons and, as a result, are deficient in solvency qualities for such materials as resins, lacquers, and others, high solvency naphthas are produced from feed stocks that have been treated in various hydrocarbon conversion processes, such as hydro-forming, to increase the aromatic hydrocarbon content of the naphtha. Thus, both aliphatic and aromatic type naphthas are made available.

The art of distillation and fractionation has been developed to such a degree that these specialized products are now produced quite readily in commercial units. Such products can sometimes be manufactured satisfactorily as sidestream cuts on crude distillation towers, but the more usual practice, where they are regular plant products, is their fractionation in special naphtha rerun units. In one typical unit, a petroleum naphtha distillate is separated by fractionation into an overhead stream, four side streams, and a residue. The overhead stream may be rubber solvent or low end point gasoline depending upon the characteristics of the charging stock. The four side streams are naphthas of various characteristics as desired. A more flexible type of special naphtha production is carried out in a superfractionation unit. This unit comprises a plurality of fractionating towers connected in series, said towers containing a large number of plates. In one particular superfractionation. installation, two towers, a primary fractionating tower and a secondary fractionating tower, each containing 66 bubble trays, are used in series. Depending upon the boiling range desired in the final product, the required feed stock is passed to the primary fractionator. The overhead vapor from this tower is condensed, a portion going to storage and the remainder being returned to the primary fractionatoras reflux. The bottoms from the primary fractionating tower passes to the secondary fractionator. Only one finished naphtha fraction is produced at a time and it is taken overhead as a heart out from the secondary fractionating tower. Obviously, the overhead fraction from the primary fractionating tower may contain desirable naphthas, as may the residue from the secondary fractionating tower. When this situation exists, the respective streams are placed in separate storage tanks and subsequently charged to the unit to produce the desired specification fraction in the established manner. A careful study of such factors as yield, purity, location of the optimum feed plate, location of fractions in the charge, and boiling points of distillates and residues is necessary in. obtaining the required operating flexibility in these units.

Economics of the process and good operating procedure require that the thus produced distillate be ready for market without further treat ing. Although, in general, naphthas should be free from acidity, non-corrosive by the copper strip test, and free from gums or suspended matter, one of the rigid specifications required of the finished special naphtha is that it be free of the objectionable odor characteristic of lower boiling petroleum mercaptans. The absence of this odor is desired in order that the olfactory sense of the consumer not be disturbed by the marketed distillate, or in order that this odor not be imparted to any manufactured products containing these special naphthas. A specification test to indicate the presence of or freedom from these mercaptans which would cause this objectionable odor is the widely used so-called doctor test. doctor test gives positive results is deemed to contain these odoriferous mercaptans and is condamned as sour. If the test is reported as negative, it is considered that the sample is substantially free from these odor-causing mercaptans and considered sweet. The essence of this invention is, therefore, directed to conforming with the requirement of this standard specificaion by l310dll6illg as a finished distillate from the naphtha rerun unit, a product requiring no furth r sw t n n If the mercaptan content of the naphtha feed stock to rerun unit is not carefully controlled by proper refining, the special products fractionally distilled from this charge may be oh specification. It has been reported that in order to PlQduce a, doctor negative or sweet product, the mercaptan content of the product must be at or below. 0.0001 per cent by weight of mercaptan sulfur. The type crude available will of necessity dictate whether a sweetening process is a necessary adjunct to the naphtha rerun system. In

processing a "sour crude, i. e. one having a high. sulfur content, in order to obtain marketable distillates, it is necessary that the distillates produced from these crudes be treated in one of the various light distillate treating processes available to the refining industry. These processes, in general, fall into three broad classifications: (1') oxidation processes, (2) mercaptan dissolving processes, and (3) catalytic desulfurization. The oxidation processes, in which the mercaptans present in the distillat are chemically converted to disulfides, produce a doctor sweet product which, due to the conversion of the foul-smelling mercaptans to less odoriferous disulfides, cannot be objected to olfactorily. Most common of this type process is the conventional sweetening with doctor solution. Other well known processes of this type are the copper chloride, hypochlorite, lead sulfide, and air oXida-' tion in the presence of a catalyst, such as a phenolic type compound. Although this type of process is losing favor as a gasoline treating process because the disulfides harm the lead sus- A sample of the product in which the ceptibility of the gasoline and also because it is no longer considered necessary that marketable gasolines be doctor sweet, it does find considerable use as a naphtha treating process because the treated product does meet the required mercaptan sulfur content specification and gives a doctor negative product. The non-oxidizing type processes aforementioned have not found wide acceptance by the industry in the treating of naphthas, other than those which are used as a constituent in the blending of gasoline, inasmuch as they generally do not give a complete sweetening effect.

Having selected the oxidation type process as the more adaptable of the type processes available because of the ability to provide a complete sweetening effect, the efiicacies of treating the naphtha charged to the rerun unit prior to rerunning or treating the finished products to give a doctor sweet product should be considered. While both practices are followed, it has been found that the method involving the treating of the naphtha feed stock prior to rerunning is more advantageous mainly because it saves scheduling of the treaters when a variety of specialized products are produced. When scheduling of the treaters is required, as is the situation when the finished product is treated, for each change in product there is an attendant loss of time and product involved due to changeover from one product to another. These difficulties are eliminated if the charge stock to the special naphtha rerun unit is treated, rather than the distillate produced. There is, however, a serious objection to this modus operandi that arises when the higher end point special naphthas are being produced. To effect these higher end point naphthas, higher operating temperatures are required. The distillate obtained under these conditions, although made from a doctor sweet feed stock, gives a doctor positive result and is, therefore, not acceptable because it does not conform with the mercaptan sulfur content specification. Before these products can be marketed, it is necessary to retreat the off-specification product. The advantages obtained by pretreating the feed stock are forced. to lie in the penumbra of the disadvantages and remain unrecognized.

It is, therefore, an obiect of this invention to present a method of producing special naphthas that conform with th mercaptan sulfur content specification with a minimum of treating. Another object is to provide a method in which a doctor sweet distillate is manufactured without retreating the desired boiling range distillate after it has been fractionally distilled from a doctor sweet naptha charge. A still further object is to provide a process for producing special na htha fractions in which a petroleum naphtha distillate having a boiling range of from about 225 to about 421 F; is sweetened in an oxidation type process, said sweetened naphtha is then rerun in a special, naptha. rerun unit to produce a specialty product that is doctor sweet without further treating. These and other objects are made apparent by the following exposition of our invention.

The objects of our invention are attained by I the production of a doctor sweet special naphtha peroxide compound which conforms to the genoral formula, R10 0 --R2, wherein R1 an organic radical and R2 is selected from the group consisting of an organic radical and hydrogen and which is stable against rapid decomposition at the temperatures reached in the distillation. Compounds contemplated by this invention are exemplified by organic peroxides, hydroperoxides, peracids, salts of peracids, perethers and peresters. It has been found that so long as the compound contains the peroxide linkage in its structure, it is eifective to improve the efficiency of the distillation operations.

Specific examples of useful peroxides of the foregoing classes are as follows: di-tertiary-alkyl peroxides, such as di-tertiary-butyl peroxide, di t-amyl peroxide, di-t-octyl peroxide, tbutyl pentamethylethyl peroxide, di-triethylmethyl peroxide, di-t-dodecyl peroxide, etc., tertiary-alkyl hydroperoxides, such as tertiarybutyl hydroperoxide, t-amyl hydroperoxide, toctyl hydroperoxide, t-dodecyl hydroperoxide, etc., di-n-propyl peroxide, isopropyl hydroperoxide, di-sec-butyl peroxide, n-hexyl hydroperoxide, naphthene and unsaturated naphthene hydroperoxides and peroxides, such as 1-methylcyclohexyl-l hydroperoxide, t-butyl l-methylcyclohexyl-l peroxide, 1-methyl-3-methylene cyclopentyl-2 hydroperoxide, 2,3-dimethyl cyclopentenyl-3 hydroperoxide, methyl cyclopentenyl peroxide, methyl 1-isopropyl-4-methylcyclohexenyl-3 peroxide, indane hydroperoxide, methyl indane peroxide, etc.,terpene peroxides such as ascaridole, limonene hydroperoxide, pinene hydroperoxide, etc., hydrogenated naphthalene peroxides and hydroperoxides such as tetralin hydroperoxide, methyl' tetralin peroxide, etc., aromatic peroxides, such as l-phenylethyl-l hydroperoxide, p-toluylmethyl hydroperoxide, etc., a hydroxy and a,a'-dihydroxy, derivatives of peroxides and hydroperoxides such as a-hYdI'OXY- heptyl hydroperoxide, a-hydroxydodecyl hydroperoxide, a-hydroxynonyl hydroperoxide, hydroxy dicarbethoxymethyl hydroperoxide, ahydroxyethyl methyl peroxide, a-hydroxymethyl ethyl peroxide, a-hydroxyethyl ethyl peroxide, (1.- hydroxyheptyl ethyl peroxide, a,a-dihydr oxydipropyl peroxide, a,a'-dihydroxydiheptyl peroxide, a,a'-dihydroxydidodecyl peroxide, a,a'-dihydroxydidodecyl peroxide, a,a'-dihydroxydiisoamyl peroxide, di (hydroxy dicarbethoxyemethyl) peroxide, etc., peresters, such as t-butyl perbenzoate, t-butyl perstearate, t-butyl perundecylenate, t-butyl diperadipate, t-butyl diperphthalate, t-amyl perbenzoate, dimethy1-, diethy1-, and diisopropyl perterephthalates, trans-9- decalyl perbenzoate, etc., acyl peroxides, such as referred to in the specification as organic per- H oxides.

Although the application of this invention is directed to the use of organic peroxides ingeneral, there are obvious practical aspects that "must be'considered. Foremost is the inherent,

properties of some of these applicable organic peroxides to decompose rapidly and violently upon sudden'heating or shock or both. Acetone peroxide, diacetyl peroxide, diethyl peroxide, di-

methyl fulvene'peroxide, ethyl hydroperoxide, 1

fumaryl peroxide, hexamethylene triperoxy diamine, methylethyl-ketone peroxidephthalyl peroxide, succinic peroxide,- and succinyl. peroxide are specific examples cited in the literature of organic peroxides that are unstable and dangerous to handle. In addition we have found that the metal salts ofhydroperoxides and peracids are not suitable for the application to our invention. "These metal salts show an extreme tendency to hydrolyze, are very explosive in the dry condition, and show little or no solubility in hydrocarbon liquids such as naphthas. These disadvantageous properties therefore also preclude the use of these compounds as suitable materials. Consideration at this point should also be given tothe possible useof other than metal salts of the hydroperoxides or peracids such as the ammonium or substituted ammonium salts. The hydroperoxides possess Weak acid characteristics and would therefore not readily be expected to form salts of this type. Peracids on the other hand because of the more acidic properties may form the ammonium or substituted ammonium type salts. The literature, however, makes no mention of the existence of these compounds and it is for this reason that these compounds are not considered within the classof operative materials employed by our invention. This invention is, therefore, directed to those relatively stable organic peroxide compounds that are comparatively safe to handle and whose solubility permits their use in operative proportions.

Obviously, no specific amount of organic peroxide that will cover all varieties of naphthas -64pounds of sulfur present in the naphtha feed stock as disulfide sulfur, the optimum quantity is best determined experimentally by making tests onsamples of naphtha that are to be subjected "to processing in the special naphtha rerun unit.

Amounts as low as 0.001 per cent by weight of vthe distillate undergoing treatment in some instances are effective. It is well, however, in view "of the possible attendant hazards that may result from the use of too large proportions of the organic peroxides, to maintain the upper limit of concentration in amounts not in excess of 0.5 per cent by weight. This limit is established as a safety measure,-however, and is not to be construed as an operational limitation.

This aspect, as well as the essence of the invention, is shown by thefollowing illustrative,

but non-limiting, examples:

Example 1.-Three hundred milliliters of a doctor sweet naphtha stock having a distillation range between 256 F. and 438 F.-and containing approximately 0.03 per cent by-weight of disulfide' sulfur (in addition to sulfur compounds other than mercaptans and disulfides) was subjected to distillation from a one-liter glass flask under conditions arranged. to give considerable residence time of the naphtha charge in the flask during distillation; The distillate started to become sourto thedoctor test when the temperature of the liquid in the flask was 350 to 360 F. In a similar distillation, except, that 0.01 per cent by weight "of' benzoyl peroxide was also scr am present. inthe. flask, the distillate began to; give positive results tothe doctor test. only when the temperature of the liquid in. the flask. was380 25.

Example 2.When the. distillation of sweetened long range-naphtha stock. was. carried out as in Example 1, exceptthat 0.01 per cent byweight of t-butyl hydroperoxide, was substituted for the benzoyl peroxide, a-s'weet distillate was separated from the naphtha charge stock in the; flask until the temperature of the liquid thefiask reached 383 F.

In further explanation. of the foregoing examples it should. be noted. that these tests were conducted in a batch distillation. Commercial installations are generally operated. continuously and under conditions whereby the. feed is introduced to the fractionators. and flash; vaporized. This procedure, which is frequently taken advantage of in the art, enablesthefeed stock contaim ing materials boiling below the temperature at which the feed is introduced to. be. fractionated andthcreby produce anoverhead; product having a much higher end point than thetemperature at which the flash vaporization was-effected. This aspect is pointed out. to. show that although a maximum temperature of. about 383 F.. was attained in the above examples if advantage is taken of the mechanism. of flash vaporization a naphtha product will. be obtained as an overhead product from the fractionators used. in the commercial manufacture of these. special naphthas that will have a much higher end: point, than the temperature at which flash vaporization occurred, that. is, the tempcrature-atwhich the feed stock is introduced. into the: fractionation units. The success of this. phenomenon depends, of course, on the. presence in the. feed of material of lower boilingpoint than said temperature.

It will. thus be seen that. we have succeeded in retarding. the formation of mercaptans during distillation, thereby yielding: a sweet distillate having a higher end; point: than. the distillate obtained when the distillation. is'carried out in the absence of the; organic peroxide; compounds of our invention.

In carrying outtheteachings of,- this invention, the effective amounts: of. organic peroxide-may be introduced into the fractionation. zone by using the naphtha feed as acarrier or directinjection. into the; distillation zone. Where. direct introduction is. employed as the. method. of application, it. is preferable: to usc a iOllltiOll'sQf the selected organic. peroxide-in a; compatible solvent, such as the feed stock to the. unit. 'Ifheresidue from thefractionating towers will contain any residue organic peroxide employed. as the distillation agent, from which-it mayberecovered, for re-use, by any suitable means.

The mechanism of. the phenomenon attributable to our invention is not readily explained. The obvious cause of the-sour distillateproduced from. a, naphtha charge stock which has been sweetened in. an oxidation type sweeteningprocess whenthe. teachings. of our invention are not followed is that mercaptans. are formed during the. distillation. operation. Mercaptan formation by the cleavage. of disulfides-is well known. and this indubitably accountsv for a. certain. amount of the mercaptanspresent. in the sour product, although other modes of. mercaptan formation from sulfur compounds. present other than: the

' disulfides may also account for the presence of mercaptans in critical amounts sufiicient. to pro- 8 mess-by carrying out the distillation process. in theprescnce of small amounts of, an organic per.- oxide.

It. will be seen, therefore, that we have been successful in providing a method whereby it is possible to separate from a naphtha feed stock, which has been sweetened in an oxidation type sweetening process, by fractional distillation in the presence. of an organic peroxide, 2. sweet distillate having ahigher end point than: a similarly produced distillate having been separated in a distillation processin which an organic peroxide was not used.

Having substantially disclosed our invention, we therefore claim:

1.. A. method for inhibiting, the increase in mercaptan content of lightpetroleum distillates containing organic sulfur compounds including disulfides during heating thereof comprising the heating in the presence of a small amount of a relatively stable organic peroxide selected from the group consisting of tertiary butyl hydroperoxideand benzoyl. peroxide at temperatures conducive to organic disulfide decomposition but below those temperatures at which the said disulfides decompose in the presence of said peroxides.

2. A method in accordance with claim 1 in which the peroxide is benzoyl peroxide.

3. A method in accordance with claim 1 in which the hydroperoxide is tertiary butyl hydroperoxide.

4. A method for separating by fractional distillation a petroleum naphtha, saidnaphthahaving been subjected to a sweetening process wherein petroleum mercaptans contained in said naphtha are converted to disulfides, which comprises conducting the distillation in the presence of a small amount of relatively stable organic peroxide selected from the group consisting of tertiary butyl hydroperoxide and. benzoyl peroxide at temperatures conducive to organic disulfide decompositionbut below those temperatures at. which the said disulfides decompose in the presence of said peroxides to produce a distillate having a mercaptan-sulfur content of not more than about 0.0001 per cent by weight and. having an end point which is of ahigher degreev of temperature than. it is possible to obtain in the absence of said organic peroxide.

5; A method in accordance with claim. 4 in which. the. peroxide. is benzoyl peroxide.

6. A method in accordance with claim 4 in which the hyd'roperoxide is tertiary butyl hydroperoxide.

7.. In amethod for. heating sulfur-containing,

ld'octor sweet, petroleum distillates boiling withheating in the presence of a relatively stable organic peroxide selected from the group consisting of tertiary butyl hydroperoxide and benzoyl peroxide. said organic peroxide being present in the ratio of 1 pound molecular weight forv each sixty-four (64) pounds of sulfur, calculated as disulfide sulfur, present in the said petroleum distillate, at temperatures conducive to. organic disulfide decomposition but below those temperatures at which. the said organic disulfidcs decompose in the presence of said peroxides.

8. A method in accordance with claim 7 in whgzhthe. organic peroxide is tertiary butyl perorxi e.

9. A method in accordance with claim '7 in which the organic peroxide is benzoyl peroxide.

10. A process for fractionally distilling a petroleum naphtha feed stock containing petroleum sulfur compounds including said disulfides to produce a plurality of distillates, said distillates respectively having a narrower boiling range than said naphtha feed stock, the improvement which comprises conducting said distillation in the presence'of a small amount of a relatively stable organic peroxide selected from the group consisting of tertiary butyl hydroperoxide and benzoyl peroxide, at temperatures conducive to organic disulfide decomposition but below those temperatures .at which the said disulfides m decompose in the presence of said peroxides, whereby the mercaptan content of the separated 10 distillates is maintained at an amount less than the mercaptan content of distillates produced fromithe same said naphtha feed stock by fractional distillation in the absence of the aforesaid organic peroxide. 1

GEORGE W. AYERS. MARCELLUS J. GEERTS. ROBERT E. CHANDLER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,840,269 Borgstrom Jan. 5, 1932 2,430,865 Farkas et a1 Nov. 18, 1947 2,472,152 Farkas et al June 7, 1949 2,497,349 Farkas et a1 Feb. 14, 1950 

1. A METHOD OF INHIBITING THE INCREASE IN MERCAPTAN CONTENT OF LIGHT PETROLEUM DISTILLATES CONTAINING ORGANIC SULFUR COMPOUNDS INCLUDING DISULFIDES DURING HEATING THEREOF COMPRISING THE HEATING IN THE PRESENCE OF A SMALL AMOUNT OF A RELATIVELY STABLE ORGANIC PEROXIDE SELECTED FROM THE GROUP CONSISTING OF TERTIARY BUTYL HYDROPEROXIDE AND BENZOYL PEROXIDE AT TEMPERATURES CONDUCIVE TO ORGANIC DISULFIDE DECOMPOSITION BUT BELOW THOSE TEMPERATURES AT WHICH THE SAID DISULFIDES DECOMPOSE IN THE PRESENCE OF SAID PEROXIDES. 